If, as classic immunology would suggest, tumor cells are rejected by allogeneic hosts as a result of either direct or indirect allorecognition of the foreign MHC/peptide complexes by the host's T cell receptors [35,36] then such allorecognition should not occur within a chimeric mouse co-tolerant for the MHC molecules of both its tissue types and cells of either of these tissue types should not be rejected. The gene discussed is HLA-C; the disease is neoplasm.